In general, in order to adjust internal pressure of a crank case positioned at a lower end portion of an engine, gas is discharged from the crank case to the outside. The gas discharged from the crank case to the outside is in a state in which combustion gas injected into a combustion chamber of an engine to thereby be combusted, unburned gas, and engine oil protecting a cylinder, a piston, and a crank shaft are mixed with each other.
When gas in which the engine oil and the unburned gas are mixed with each other is continuously discharged to the outside, an exchange period required to change the engine oil is shortened, which may have a negative influence on maintenance of a vehicle and fuel efficiency.
Therefore, according to the related art, as illustrated in FIGS. 1 and 2, an oil separator 1 according to the related art separated engine oil from gas G discharged from a crank case to the outside to re-inject the separated engine oil into an oil pan 2 provided in an engine. In this case, gas from which the engine oil was separated was re-circulated into an intake manifold 3 so as to assist in improving fuel efficiency.
However, as illustrated in FIG. 2, a size of the oil separator 1 separating the oil from the gas discharged from the crank case according to the related art has been continuously increased in order to increase an amount of treated gas and engine oil separation efficiency, such that it has been difficult to secure a space for mounting the oil separator 1 in the engine, and an internal structure became complicated. Therefore, it was difficult to manufacture the engine, a manufacturing cost was increased, and a weight was increased, which had a negative influence on fuel efficiency.